Now, I have a few questions. The meter itself has only been calibrated once in its lifetime, will cal-labs still calibrate this meter?
Yes, e.g. Gossen-Metrawatt calibrates old Siemens meters. 113 Euro + VAT, and probably some expensive shipping, too. http://www.gmci-service.com/en/general.html (http://www.gmci-service.com/en/general.html)Ouch. Thats expensive. Do you happen to know of anyone in the USA or North America?
Get yourself a cheap voltage reference, power up the meter and see how it does. I wouldn't be surprised if it is still within the 1-year accuracy specs. If it is not, open it up and adjust the appropriate pots on the PCB. I doubt that this meter can only be calibrated through software, but it is possible. That would save you a load of money and postage fears.
Try to upload as much of the manual as you can and if you open it up, take some pics of the PCB.
Also, some interesting behavior I noticed: The meter basically requires almost brand new fresh 9v batteries.On a multimeter that I was trying to fix, I found that my brand new 9V battery died in almost 4 hours. Then I decided to measure the current draw and was surprised to see the multimeter draw 85mA when I expected around 1mA.
On a multimeter that I was trying to fix, I found that my brand new 9V battery died in almost 4 hours. Then I decided to measure the current draw and was surprised to see the multimeter draw 85mA when I expected around 1mA.
You may want to see what the current draw is?
In addition, carefully check the capacitors for any leakage from the bottom.
Upload the schematics and someone may be able to help you.Ok, got around to doing it today. I measured the mA. When turning the meter on the initial spike is ~5.0mA to 5.9mA. It then settles near 2.0mA, as soon as that happens the screen starts to fade away.
I would first confirm all circuit voltages are normal then test or replace the old electrolytic caps.
If the battery current draw is higher than 10mA, suspect that something has shorted on the PCB.
Everyone has different techniques to troubleshooting so what I'm suggesting is my method.Should I measure the VDD and VSS at the lcd controller? That is the UDP chip you linked the datasheet to. Part of the problem in doing that is that the chip is actually an SMD, but its mounted underneath the display. The display is glued on with epoxy to some zebra strips. So getting to the chip would require me to basically ruin the screen assembly. I can measure the voltage from the op amp though, as it isn't covered by the display.
1) The datasheet for the main IC is at
http://pdf1.alldatasheet.com/datasheet-pdf/view/128483/NEC/UPD7514G-12.html (http://pdf1.alldatasheet.com/datasheet-pdf/view/128483/NEC/UPD7514G-12.html)
I usually take a cursory glance, which I have not done while writing this, to see how it works in general.
2) I like to take voltage readings. VDD and VSS are "obvious" choices to me. Are these readings stable?
I also see in the schematic there are some TP (test points). I suggest taking voltage measurements and reporting them.
3) It is my understanding, that most lcds work require 3V in order to display something. When the meter displays something, I'm assuming the voltage at the lcd pins is around 3V and when it fades away, the voltage is well below 3V?
4) The 5mA and 2mA current draw sound reasonable right now.
Should I measure the VDD and VSS at the lcd controller?I would measure VDD in as many places as possible as shown in the schematic just to make sure there are no open pcb traces/tracks, bad capacitors affecting VDD, open resistors, shorted transistors, etc.
Ok, so I'm having some problems with the meter. I bought a fresh pack of batteries and the meter doesn't work as expected.Let me see if I understand... you have a meter that you know from other tests does not work correctly. Continuity shows shorted test leads when they are not. Volts shows nothing. ... all signs point to an internal short circuit (maybe a failed input protection device) ... so you decide to stick the leads into a 120 VAC household power socket? :palm:
I ended up taking it apart and cleaning the rotary switch with isopropyl alcohol. But this hasn't helped. If I leave the rotary switch in the ohms/resistance/continuity settings and power it on, the display works, but the meter wont measure any resistance. If I set it to continuity, the meter detects that there is a closed circuit, when there is none.
Setting the rotary switch to Volts, Temp, Amps, or frequency nothing happens. If I switch it on in one of these settings the display comes on for about 1 second and then disappears.
Any thoughts? I also managed to get a AC voltage while playing with the unit. Turning it on and off repeatedly occasionally makes it 'work'. I measured what was supposed to be a 120v AC voltage, but the meter read exactly half the value ~60v.